Television receiving system



1930- P. T. FARNSWORTH 1,773,931

TELEVIS ION RECEIVING SYSTEM Original Filed Jan. 7, 1927 reams aag. as,resin P3110 '1'. rnnnswonrm or BERKELEY, osriroanm, .assieiror lsr amassassronmnnrs, ro rnLEvIs'IoN LABORATORIES, mo, or SAN raanorsco,eenrromrm, a

con'romrron' or. oauronnra TELEVISION RECEIVING SYSTEM Originalapplication filed January 7, 1927, Serial No. 159,550. Divided and thisapplication filed November 7, 1927. Serial No..231,691.

My invention relates to television, and particularly to the reception ofpictures or views transmitted by radio. The receiving system comprisingmy invention is especially adapted for receiving pictures transmitted asdescribed in my co-pending application, Serial No. 159,540, filedJanuary 7, 1927, of which this is a division.

An object of my invention is to provide a receiving apparatus of generalusefulness in television systems.

Another object of my invention is to provide an apparatus for receivingradio television waves of the type generated by the apparatus describedin my co-pending application above mentioned.

A further object is to provide a system for scanning a field in twodimensions, operative by a single wave.

My invention possesses other objects and valuable features, some ofwhich will be set forth in the following description of my inventionwhich is illustrated in the drawings forming part of the specification.It is to be understood that I do not limit myself to the showing made bythe said description and drawings, as I may adopt varying forms of myinvention within the scope of the claims.

Referring to the drawings:

Fig. 1 is a diagrammatic view of the optical system and light valve.

Fig. 2 is a circuit diagram of the receiving apparatus.

In terms of broad inclusion my invention comprises circuits forreceiving and detecting the radio wave upon which two components aremodulated. One of these components is utilized to modulate a light beam.The other component, itself a modulated wave, is operative to cause thelight beam to scan a field of View in one direction. A second detectorcircuit simultaneously detects this latter wave, separating out themodulating component, which is used to scan the field in anotherdirection.

In terms of greater detail the apparatus of my invention is constructedand operates as follows: Preferably there is employed a source of lightof constant intensity, such'as an are light 6 and to obtain a pencil oflight therefrom, there is placed a shutter 7 with a small aperture 8 infront of the are light. The light from said shutter is then passedthrough a polarizcr 9. The polarizer is indicated as preferably in theform of a Nicol prism. The polarized light from the Nicol prism 9 isthen passed through a lens 11 which parallels the polarized light andthe parallelled light is then passed through a device for rotating theplane of the polarized light. This device may be any device suitable forrotating the plane of the polarized light in accordance with thefluctuations of the light current received at the receiver. The methodof receiving and separating this light current from the transmitted wavewill be hereinafter pointed out. The preferred form of such device isillustrated as comprismg a means for producing a magnetic fieldfluctuating in accordance with the light current, such as the coil 12,surrounding an electrically optically active medium 13, such for exampleas a thin film of iron, cobalt, or nickel, or carbon disulfide, glass,or any other material in which a. beam of polarized light rotatesconsiderably when subjected to a magnetic field. I prefer to employcarbon disullide and said carbon disulfide is held in the core of thecoil 12 by glass plates 14:.

The light from the light rotator is then passed through a device adaptedfor restricting the passage of light in accordance with its degree ofrotation. T preferably employ a combination of a pair of gratings 16 and17 and a iii-axial crystal 18. The gratings 16 and 17 may be any usualform of light gratings, for example, ruled upon a silvered transparentsurface, and are placed at opposite ends or sides of the bi-axialcrystal with their gratings opposed. The bi-axial crystal employedbetween the gratings is adapted to produce a conical refraction of thelight. As an example of a suitable crystal of this kind, I have employeda crystal of arragonite one centimeter thick between the gratings ruledwith 100 lines per millimeter. With this combination, the rotation.between com plete extinction and complete restoration is of the order oftwo degrees. Thus with this analyzer, very small currents may beemployed upon the rotator, permitting the use of a coil of very highnatural period.

In explanation of the action of the bi-axial crystal 18, it isunderstood that the light is directed on said crystal along one of itsoptic axes. When this is done, the light is refracted to an extentdepending on the position of the plane ofpolarization. When unpolarizedlight from an aperture is directed on such a crystal along one of itsaxes, said light will appear as a circle from the other side of thecrystal, butwhcn a beam of polarized light is directed along one of theaxes of the crystal, it appears as a point of light lying in the circleproduced by the unpolarized light, but its position is dependent on theposition of the plane of polarization of the beam of light. A 90 degreerotation of the plane of polarization of the beam of light will rotatethe light from the crystal from one side of the circle to the oppositeside. During the passage of the light through the bi-axial crystal, thewave front of the beam of light remains parallel and the wave front ofthe beam passes through perpendicularly to the optic axis of thecrystal.

The beam of polarized light passes from the rotator to the grating,where a portion is intercepted or occluded, and then passes into thebi-axial crystal 18. fracted in the crystal in a direction dependingupon the plane of polarization, this being so adjusted that the plane inwhich it is refracted is approximately parallel to the lines of thegratings. The shadow of the grating 16 therefore falls upon grating 17,and if the shadow of the bars of grating 16 fall upon the interstices ofgrating 17, the beam will be wholly occluded. If, however, the plane ofpolarization be rotated slightly the plane of refraction in crystal 18will change and the shadow will move, and when the movement is such thatthe shadow falls upon thebars of grating 17 a maximum of light istransmitted.

By means therefore, of the polarizer 9, light rotator, and analyzercomprising the gratings 16 and 17 and the bi-axial crystal 18, theconstant supply of light through are light 6 is caused to produce alight of varying intensity, varying in accordance with the intensity ofthe light current supplied to the coil 12. Thereby, without theemployment of any mechanical moving apparatus, the light current isrcconverted into light.

Such light is then passed through a lens 19 by which it is focused upona pair of cooperating oscillographs 21 and 22. Said cooperatingoscillographs 21 and 22 are positioned at right angles one to the otherand so that the light from one strikes the other oscillograph. Saidoscillographs are operated at different frequencies with the result thatthe light is by said oscillographs projected in horizontal vibrations,which are The light is re-' successively lowered or. raised verticallyso that the light can pass through a lens 23 upon a screen 24 and coverssuccessively an entire rectangular area' of said screen. Theoscillographs '21 and 22 are operated by electrical currents of thefrequencies of the two analyzer currents used in scanning at thetransmitteigas described in my copending application above mentioned, sothat the passage of the beam of light over the screen 24 is insynchronism with the bending of the electrical discharge from thesensitive plate of the photo-electric cell and thereby each portion oflight is properly co-ordinated to produce a correct image of the objectbeing transmitted.

Referring to Figure 2, the electrical apparatus for receiving thetransmitted wave in the transmitter and correctly applying the lightcurrent and analyzing currents to the light rotator and oscillographs isas follows: 26 indicates a receiving antenna or other means forcollecting wireless waves, which antenna is connected through aninductance 27 to a ground indicated at 28. Inductance 27 forms a primaryof a transformer in which the secondary 29 is in the grid circuit of adetector 31. 32 indicates a tuning condenser for bringing the receiverin resonance with the carrier wave of the transmitter. The plate 33 isindicated as connected to a plurality of filters, the first of whichcomprises the inductance 34, the voltage across which is supplied to thegrid of a second detector 36. The first filter comprising the inductanceshould be receptive of the first carrier wave developed in thetransmitter. There is thus imposed upon the grid of a detector tube 36 apotential developed by the light current modulated upon the firstcarrier wave formed in the transmitter. In the detector 36, such carrierwave is detected to produce a current output from the plate 37, which isequivalent to the light current developed in the transmitter. In thesecond detector circuit 36, reference character 38 indicates a.condenser for passing the high frmpiency and blocking the low frequencycurrents, and 3.) indicates a battery for supplying the. platepotential. The plate 37 is indicated as connected with the coil 12 ofthe light rotator.

The. complete output circuit of the detector tube 31 also includes acondenser 41 of a capacity suitable for by-passing the high frequency ofthe first carrier wave which is detected by the tube 36 and of acapacity to block the frequency of the analyzing currents. Suchanalyzing currents are therefrom passed through a choke 42 and line 43to one of the oscillographs 22. said oscillograph being connected by aline 44 with a resistance 46 shunted across line 43. and line 47 whichline connects with the opposite side of the condenser 41. By thisconnection, the oscillograph 22 is operated by the higher analyzingfrequency, e. g., a 500 cycles per second frequency. Said frequency alsopasses through the grid condenser 48 and leak 49 to a grid 51 of adetector tube 52 wherein said frequency is detected to deliver from itsplate 53 a potential of the frequency of the first analyzing current,say 10 cycles per second. The plate 53 is indicated as connected by theline 54 to the resistance 56 which is connected b a tap 57 to theoscillograph 21 and the osci lograph is indicated as connected by line58 through the battery 59 to the filament 61 of the detector 52. Thefilament 61 is also connected by the lead 62 with the condenser 41. Theresistances 46 and 56 provide a means for controlling the potential ofthe currents applied to the oscillographs.

It will be readily apparent from the description of the apparatus andoperation.

thereof, how the detected light current imposed upon the coil 12modulates the light in accordance with the intensity of light at theparticular point from which said light current originated from the lightsensitive plate of the transmitter described in my co-pendingapplication, Serial No. 159,540. It will also be seen that said light isprojected upon the screen 24 by the oscillations of the oscillographs 21and'22 to form a correct image of the objecttransmitted, the lightbeing" caused to travel back and'forth across the screen similar to theaction of the shutter of the transmitter, making in the example given500 reciprocations across the screen in covering the complete areathereof, and said re ciprocations are made Within a period of 1/20th ofa second. It is understood, however, that the process and apparatus ofthe present inventlon is not necessarily limited to the use of theparticular frequiencies given for the purpose of facilitating thedescrip tion of a preferred process and apparatus.

The process and apparatus of the present invention permit the selectionof such small elementary areas of the image to be transmitted that theproduced image on the screen 24 follows'all of the light shades of theobject, producing a correct image thereof. This is accomplished withoutthe employment of mechanically moving parts, excepting the vibratingstrips of the oscillographs. The zip paratus is thus free frommechanical problems.

While the process and apparatus for producing television hereindescribed is well adapted for carrying out the objects of the presentinvention, it is understood that various modifications and changes maybe made without departing from the invention, and the invention includesall such modifications 1. In television reception, the method ofscanning which comprises traversing the field of view in one directionwith a modulated wave, detecting said wave, and traversing the field inanother direction with the detected component of the wave.

2. In television reception, the method of scanning which comprisestraversing the field of view in one dimension with a modu lated wave,detecting said wave, and traversing the field in the other dimensionwith the detected component of the Wave.

3. In a television receiver a detector, input and output circuits forsaid detector, a scanning device operatively connected to said in putcircuit, anda second scanning-device operatively connected to saidoutput circuit.

4. In a television receiver an audion, input and output circuits forsaid audion, a scanning device operatively connected to said inputcircuit, and a second scanning device operatively connected to saidoutput circuit.

5. In a television receiver, a detector, input and output circuits forsaid detector, an oscillograph element operatively connected to saidinput circuit, and means in said output circuit cooperating with saidoscillograph element to produce a picture.

6. In a television receiver, a detector, input and output circuits forsaid detector, and oscillograph elements operatively connected to saidcircuits. r

7. In a television receiver, a circuit carrying a complex wave, adetector actuated by one component of said wave, a light valve in theoutput circuit of-said detector, a scanning device operable by a secondcomponent of said wave, a second detector, actuated by said secondcomponent, and a second scanning device in the output circuit of saidsec ond detector. I 8. In a television receiver, a circuit carrying acurrent comprising two components, one of said components being amodulated wave, means operable by one of said components to produce amodulated beam of light, and scanning means operable in one direction bysaid Wave, and in another direction by the modulation thereof.

9. In a radio television receiver, a detector having an output circuit,a circuit deriving from said output circuit, operative means in saidderived circuit for producing a modulated light beam, a second circuitderiving from said output circuit, and operati've means in said secondderived circuit for causing said beam to scan a field. Y

10. In a radio television receiver, a detector having an output circuit,a circuit deriving from said output circuit, a second detector in saidderived circuit, and an output circuit for said second detectorcomprising means for producing a modulated beam of light.

11. In a radio television receiver, a detector having an output circuit,a circuit deriving from said output circuit, a second detectorin saidderived circuit, and an output circuit for said second detectorcomprising means for modulating a beam of light from a constant source.

12. A device comprising ajpolariz'er, a' lightrotator receivingpolarized light therefrom, means for refracting thelight in accordancewith its degree of rotation, and

means for coordinating successive portions of light to form a picture.

13. A device comprising a polarizer, 21.

I light rotator receiving polarized light therefrom, means forrefracting the light in accordance with its degree-of rotation, a plurality of gratings for diverting light in-accordance with its degreeofrotation, and

means for coordinating successive 'portionsof light to form a picture14. In a television receiver, a detector, input and output circuitsforsa'id detector, a scanning device directly connected. to said inputcircuit, and means in saidoutput circuit cooperating with said scanningmeans 'toform a picture.

In test mony whereof; have hereunto. setmyhand. r

' PHILO T. FARN SWQRTH.

